This is a feature in that "gee, I wish I'd of thought of that" category. The latest update to the TomTom app (version 1.5) lets you select any photo that has been geo-tagged and navigate to that location. It's great for finding that favorite picnic spot, or that great photo location.
I tried the feature out today, navigating to 2 locations I had in my iPhone photo roll. In each case, the app showed a map of the location, and with a couple of clicks I was on my way.
The app also now supports the iPhone 4 Retina display and the speed of the app is supposed to be faster but I didn't see anything dramatic. TomTom U.S.A and U.S. & Canada apps are currently available for $49.99 and $59.99, respectively. It's a really full featured way to navigate. Navigating to a photo is a really great idea, and I'd like to see some of the other nav apps add this feature as well.